211 
Dr. Hosack's Observations on Vision. 
anterior part of the eye, we have seen the situation of those 
muscles ; the recti strong, broad, and flat, arising from the back 
part of the orbit, passing over the ball as over a pulley, and in- 
serted by broad flat tendons at the anterior part of the eye ; 
the oblique inserted toward the posterior part, also by broad 
flat tendons ;• when they act jointly, the eye being in its hori- 
zontal position, it is obvious, as every muscle in action con- 
tracts itself, the four recti by their combination must neces- 
sarily make a compression upon the different parts of the eye, 
and thus elongate its axis, while the oblique muscles serve to 
keep the eye in its proper direction and situation., For my 
own part, I have no more difficulty in conceiving of this com- 
bination of those muscles than I have at present of the diffe- 
rent flexors of my fingers in holding my pen. But other cor- 
responding effects are also produced by this action ; not only 
the distance between the anterior and posterior parts of the eye 
is increased, but of consequence the convexity of the cornea, 
from its great elasticity, is also increased, and that in propor- 
tion to the degree of pressure, by which the rays of light pass- 
ing through it are thence necessarily more converged. But 
another effect, and one not inconsiderable, is, that by this 
elongation of the eye, the media, viz. the aqueous, crystalline, 
and vitreous humours through which the rays pass, are also 
lengthened, of consequence their powers of refraction are 
proportionably increased ; all which correspond with the ge- 
neral principle. It may however be said, that as the four 
recti muscles are larger and stronger than the two oblique, 
the action of the former would overcome that of the latter, 
and thus draw back the whole globe of the eye ; but does not 
the fat at the posterior part of the orbit also afford a resistance 
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